Rapid process for tanning hides



United States Patent 2,955,904 RAPID PROCESS FOR TANNING HIDES Desiderio Schnoller, Pueyrredon Ave, 1256, Buenos Aires, Argentina No Drawing. Filed Sept. 11, 1956, Ser. No. 609,075

11 Claims. (Cl. 894.21)

The present invention refers to a rapid process for tanning hides and more particularly to a new form of tanning in which the fixing of the tannin is performed in a manner to shorter the process in such a measure that its adoption in the industry will impose itself so as to totally sup plant the common method of cycles as well as the most rapid methods known up to date.

As is known, the present slow methods taking several months, employ aqueous solutions of vegetable tanning materials, in which the hides are submerged until the saturation of the hide substance by the tannin, followed by the retanning, oiling, etc., in drums, where the treatment is completed.

There exist also many tanning methods in which are generally employed solutions of vegetable tannic extract of increasing concentration, which last several days or even weeks.

In these processes are used different kinds of auxiliary products, high tannin concentrations and mechanical movement of the liquid as well as of the hides submitted in order to obtain a rapid penetration of the tannin and shorten by every means the length of the process. However, leather chemists, as well as tanner-s in general,"do not advocate this accelerated system, as the results are not always promising, as in most cases the leathers are deficient through the irregularity of their texture, their short fibres, lack of elasticity, small resistance to breakage and wear, as well as their predisposition for absorbing water, apart from the bleeding in water.

This means that the rapid method is generally remote from the ideal conditions which must present well tanned leathers, as in same the fibres are generally long, there is uniformity of tissue, great elasticity, high resistance to breakage and wear, irreversible fixing of tannin and impermeability. It may be added that a well tanned leather presents a well known analytical chemical composition as to humidity, ash and fat content, hide substance, fixed tannin, water soluble matter, etc., and furthermore, its physical characteristics such as water absorption, resistance to breakage, wear, etc.

It is to be imagined, therefore, that the acceptance of this innovation in vegetable tanning will result in uniting the eminently good condition of the leather obtained, with the ultra rapid process of this method. Apart from the quality, the yield is considered as very high with great advantages in every sense.

This new method comprises a preparation of the hide in such a manner that the absorbing of the tannin is carried out by the avidity of the proper tissue, so that the tanning may be effected in a few hours without afifecting the fibres and obtaining all the qualities of a well tanned leather.

To this end, the hide is submitted to a treatment con- I sisting of three diiferent steps. The first comprises the separation of the fibres of the hide by pretanning; the second consists in submitting the pretanned hide to dehydration so as to render it avid in order to absorb-the tanning materials and the third can be classified as that Patented Oct. 11, 1960 ice of the real tannage as, in a rotative drum the vegetable tannic extracts are incorporated in the necessary proportion so that from three to five hours the hide is transformed into a practically perfectly tanned leather. After this tannin operation follows the bleaching, oiling and finishing operations, as in the same drum are added the auxiliary chemical products employed to this end.

Apart from what has been stated, several are the objects pursued by the present invention, amongst which may be mentioned the fact of obtaining a complete tanning of hides in only one operation, after same have been duly prepared, giving it the name of mono-phase tannage as unique of its kind.

Another object is that of obtaining a mono-phase tannage with the necessary previous preparation so that the process may be carried out in a few hours with equal sufliciency to that obtained through old processes in several weeks or months.

Another object is that of reducing to a minimum the duration of manufacturing since, as the tanning is done in a few hours, the total elaboration including preliminary beam-house work, can only consume 8 or 10 days, which less capital in order to set up the tanning industry. In

a daily production of soles, instead of needing a stock of 3,000 to 12,000 hides in operation, with this new method the requirements are only of 800 to 1,000 hides for the same end.

Another object is that of occupying a minimum of space for the tanning, as in this system there are no vats, handlers, rockers, layers, etc, which 'are generally destined for long treatment.

A further object of the invention is that of reaching a maximum economy in the consumption of the vegetable tanning material, as by this new method there is no loss of tannin due to precipitations or fermentations, and it is used in a rational and strict manner, the tannin product being applied in exact proportion to that which the hide substance can absorb without any loss whatsoever.

Another object is that of offering an industrial tanning basis with an appreciable saving in labor and power, as the handling is greatly reduced, as well as the moving of hides or the liquors from one vat to the other, variations in the concentration of the baths, removing exhausted liquors, cleaning of the vats, purification of the residuous liquors, etc.

Yet another object is that of operating with vegetable tanning extracts strictly calculated so that the hide submitted to same may absorb it, which means that they do not require increased concentrations of rtannic solutions nor any excess of tannin. 7

Another object is that of oifering a good vegetable tanning for any kind of hides, especially for cattle hides employed in the shoe industry, soles, insoles, belts, straps, saddlery, furniture leather, linings, splits, etc. j

The other objects of this invention will be shown throughout the following specification explaining the different steps of the process.

The beam-house work (wetting, liming, unhairing, fieshing and then the deliming) is already known and does not intervene in the specification of the present invention. Y

The three steps which are indispensable for the development of the process are the following:

, (1) Separation of the fibres The well known operation in the beam-house such as wetting, liming, unhairing and fleshing is done in the routine form, apart from the washing and deliming which are also done in the common manner.

- a w 3 The' delijned hide now called pel is now submitted to a pretanning process by separating the fibres, in which several treatments may be employed as follows:

(a) The hides may be pickled that is, treated with commonsalt and a strong acid such as sulphuric acid or muriatic acid. A general manner of pickling the hides is that of employing: lOOparts oicold water, 12 parts of salt and 1 or 2 parts of sulphuric acid on 100 parts of pelts forming a solution which is contained in a rotative drum where the hide is treated during one hour.

The hides thus pickled may be submitted to pretanning through a synthetic tannin such as that obtained by condensation ,of naphthalin-sulphonic acid with formol. Other synthetic materials may also be used such as those obtained through condensation of phenol-sulphuric acid with urea and formol. The amount of synthetic tannin employed must not surpass on the weight of the pelts. This pretanning is efi ected in a rotative drum during two or three hours. a

, (b) In orderto achieve the separation of the fibres through the pretanning, the pickled hide is treated with a solution of chromium salt of 33% basicity, using 1% of chromium oxide calculated on the weight of the pelts. Theseparation of the fibres is obtained at the end of 3 or 4' hours. f (c) The same effect is obtained by pretanning with quinone; in this case the hides are not pickled but are treated with 1% of quinone at a pH 8 in a bath of 100% of water during one hour.

(d) In another example of pretanning, this can be donegby formaldehyde, employing 1% of it at a pH of 8. The quantity of water in the bath must be 100% of the weight of the pelts. In this case the hides must not be pickled.

. (e) Other methods of pretanning may be employed such as alum or sulphur tannage or synthetic resins, etc. Fundamental isthe separation of the fibres as Well as avoiding the contraction of the grain of the hide, preparing adequately the hide for dehydration process which is to follow and leaving same in the best condition for the absorption of'the tannic extract which is the third and true process of tanning.

(2) Dehydration of the pretanned hide After pretanning, the hide must be dehydrated as, the leastwater it contains, more rapid will be the penetration and fixing of the tanning operation. For this reason the pretanned hide is submitted to a mechanical dehydration in a press to remove water in an amount at least equal to 30% based on the weight of the pelt. Preferably, its weight will be reduced to approximately one half of the original weight of the pelts due to the loss of water.

(3 Tanning The pretanned and dehydrated hides, according to points l and 2, are submitted to tanning in a unique operation which also comprises the bleaching, oiling and finishing of the leather according to its fundamental characteristics;

The pretanned hide absorbs all the tannin due to the avidity resulting from the mechanical dehydration; this happens in the lapse of 3 to .4 hours. After said absorption, the common ingredients for bleaching, oiling, finishing, etc., are added so that the tanning is completed in excellent condition in only one operation. For the bleaching oxalic acid, for oiling sulphonated oils, for finishing sulphate of 'm'agnesia, fixing agents, etc., may beused..

The incorporation of tannic extract in the hide is integral and the bleaching and roiling, etc., processes are effected in continuous and-no1mal manner, so that the hides are tanned and finished inbetween 4 to 5 hours. After this they are taken out of the drum and set out, in which state oil is applied to the grain and thereafter exposed to drying. When they are dry, they are rolled in the usual manner. a

The most extraordinary part of the invention is the a manner in whichwthe vegetable tanning is accomplished,

Tothis end, the hides are placed in the rotative drum withoutadding water or liquids of any kind, as the dehydrated condition must be maintained so that the vegetable tanning extract can occupy the-place left vacant by the previously'extracted water. In that state, powdered tannic extracts are incorporated, such as 'quebracho'extract,

chestnut extract, -mimosa extract, lignin extract or other tannic extracts employed in the tanning process, such extractsbein'g. also mixed together so as to give the needed character to the leather.

In the case of'bisulphited and pulverized quebracho ex- 7 tract, the quantity of extract required forsole-leather varies between 40 to 55% calculated on the weight of the pelts. Instead of applying same in powder, the tannic extracts can also be liquid with a concentration of 25 B. The quantity of added extract, must not be greater than that which can be absorbed by the hide substance.

that is: the incorporation of tannin for, in given circum stances in which it is applied, the development is ultra rapid and even if employed in liquids, it may be said that .the process is a dry process for, instead of a bath, it is the simple application of a tanning matter which is totally absorbed by the hide due to the avidity given to same through the mechanicaldehydration after the pretanning operation. The dehydrated hide represents a technically dry protein, whilst the tannic extract, either in powder or in very concentrated liquid, also can be considered as technically dry as there is no matter left over and it is totally absorbed by the hides. Both materials, that is the tanning extract and the substance to be tanned, react with great ease, rapidity and perfection. As there is only one step to be carried out after pretanning and dehydrating operations, the reaction may be classified as monophasic or single-phase vegetable tanning or rather as a monophasic tanning without the presence of free water, which results in an unknown phenomenon in the leather industry.

7 It is to be imagined that this simple process, of great rapidity and efiectiveness is apt to supplantthe old systerns with vegetable tanning baths of progressive concentrations and lengthy methods which extend for weeks and even months. 7

Notwithstanding that this invention can be applied to any kind of hides, the examples stated above have been directed to the elaboration of sole leather- A'concrete example is given below of the complete process from the beginning:

40 steer hides which have been submitted to the normal operation of the beam-house (wetting, liming, fleshing, washing, deliming) weigh in the pelt state 1000 kilograms. To said 40 hides a bath is given for pretanning in a rotative drum; said bath comprises in respect to the weight of the pelts the following:

'12% of salt; kilograms 1.5% of sulphunic acid; 15 kilograms In this bath the hides are drummed during two hours. After that is. to be added: 7

4% of a chromium salt with a 33% basicity corresponding to l% (C1'203); that is 40 :kilograms. This treatment must also last 3 hours.

. At the end of these last three hours, to the bath is added 0.8% of bicarbonate of sodium, that is -8 kilograms in order to basify the chromium salt during another hour. Then is to be added 2% of a synthetic tannin which is the condensation product of sulphonic acidonaphthol with formol, and sold under the trade name Tanigan PC, that is 20 kilograms, during two hours,

after which time the hides are considered as pretanned.

weigh approximately 500 kilograms.

In this condition the hides are introduced in an empty rotative drum to which is added 50% (500 kilograms) of powdered bisulfited quebracho extract. The extract is absorbed by the avidity of the hides in a period of about 3 hours; the rotation of the drum must be approximately of 18 revolutions per minute.

Through the friction of the hides, these reach an approximate temperature of 50 degrees Celsius. After this tanning process, at intervals of 20 minutes are added in the drums containing the leathers the following matter:

1% or kilograms of sulphate of magnesia 0.2% or 2 kilograms of oxalic acid jointly with 0.5% or 5 kilograms of powdered sodium bisulfate 1.2% or 12 kilograms of sulphonated oil When the ingredients, which have been incorporated to the drum, have been integrally absorbed by the leathers, these are taken out of the drum, are piled until the next day, then they are set out by a machine, are oiled on the grain side and are hung in the dryer. When thoroughly dry, they are then dampened and rolled, giving same the finishing touches.

Within the terms of the appended claims, various modifications may be made without departing from the scope or principles of this invention.

I claim:

1. A process for tanning hides comprising the steps of partially tanning the lt'des with a non-vegetable tanning agent for several hours to separate the fibers, mechanically expressing water from the partially tanned hides to reduce the weight of the partially tanned hides to an amount at least 30% less than the original weight of the hides, and tanning the hides with a vegetable tanning extract selected from the group consisting of dry, powdered tanning extracts and concentrated solutions thereof for several hours until the tanning extract has been absorbed by the hides in an amount about equal to the weight of the water removed during the expressing step.

2. A method as recited in claim 1 wherein the nonvegetable tanning agent is selected from the group consisting of syntans, chrome tanning agents, quinone, formaldehyde, alum and sulphur tanning agents.

3. A method as recited in claim 2 wherein the weight of the partially tanned hides is reduced to approximately 50% of the original weight of the hides.

4. A rapid process for tanning hides comprising the steps of partially tanning the hides with a non-vegetable tanning agent selected from the group consisting of syntans, chrome tanning agents, quinone, formaldehyde, alum and sulphur tanning agents, for several hours to separate the fibers, mechanically expressing water from the partially tanned hides to reduce the weight of the partially tanned hides to an amount at least 30% less than the original weight of the hides, and tanning the hides with a vegetable tanning extract selected fiom the group consisting of dry, powdered vegetable tanning extracts and concentrated solutions thereof of at least about 25 Baum for several hours until the tanning extract has been absorbed by the hides in an amount about equal to the weight of the water removed during the expressing step.

5. A rapid process for tanning hides comprising the steps of partially tanning pickled hides for several hours to separate the fibers with a syntan in an amount not exceeding 5% of the weight of the hides, mechanically expressing water from the partially tanned hides to reduce the weight of the partially tanned hides to an amount at least 30% less than the original weight of the hides, and tanning the hides with a vegetable tanning extract selected from the group consisting of dry, powdered vegetable tanning extracts and concentrated solutions thereof of at least about 25 Baum for several hours until 6 the tanning extract has been absorbed by the hides in an amount about equal to the weight of the water removed during the expressing step.

6. A method as recited in claim 5 wherein the syntan is selected from the group consisting of the condensation product of naphthalene sulphuric acid with forrnol and the condensation product of phenol sulphuric acid with urea and fonnol.

7. A rapid process for tanning hides comprising the steps of partially tanning pickled hides for several hours to separate the fibers with a solution of a chromium salt of 33% basicity using about 1% of chromium oxide based on the weight of the hides, mechanically expressing water from the partially tanned hides to reduce the weight of the partially tanned hides to an amount at least 30% less than the original weight of the hides, and tanning the hides with a vegetable tanning extract selected from the group consisting of dry, powdered vegetable tanning extracts and concentrated solutions thereof of at least about 25 Baum for several hours until the tanning extract has been absorbed by the hides in an amount about equal to the weight of the water removed during the expressing step.

8. A method as recited in claim 4 wherein the nonvegetable tanning agent comprises quinone in an amount about 1% of the weight of the hides, said partial tanning being performed at a pH of about 8.

9. A method as recited in claim 4 wherein the nonvegetable tanning agent comprises formaldehyde in an amount about 1% of the weight of the hides, said partial tanning being performed at a pH of about 8.

10. A rapid process for tanning hides comprising the steps of partially tanning the hides with a non-vegetable tanning agent selected from the group consisting of syntans, chrome tanning agents, quinone, formaldehyde, alum and sulphur tanning agents, for several hours to separate the fibers, mechanically expressing water from the partially tanned hides to reduce the weight of the partially tanned hides to an amount at least 30% less than the original weight of the hides, and tanning the hides with a vegetable tanning extract selected from the group consisting of dry, powdered vegetable tanning extracts and concentrated solutions thereof of at least about 25 Baum for several hours until all the tanning extract has been absorbed by the hides, said tanning extract being used in an amount about equal to the weight of the water removed during the expressing step.

11. A rapid process for tanning hides comprising the steps of pickling said hides, treating said hides for several hours with 4% of a chromium salt solution having a 33% basicity equivalent to 1% chromium oxide based on the weight of the hides, then treating the hides with about 2% based on the weight of the hides of a condensation product of sulphonic acidonaphthol with formol, mechanically expressing water from the treated hides to reduce their weight by about 50% of the original weight of the hides and then tanning the hides with a powdered vegetable tanning agent in an amount about equal to the weight of the water removed.

References Cited in the file of this patent UNITED STATES PATENTS 1,621,612 Tullis Mar. 22, 1927 1,953,968 Merritt Apr. 10, 1934 2,017,453 Bell Oct. 15, 1935 FOREIGN PATENTS 1 18,155 Australia Mar. 2, 1944 OTHER REFERENCES McLaughlin et a1.: The Chem. of Leather Manufacture, 1945, p. 588, Rheinhold Pub. Co., N.Y.C. 

1. A PROCESS FOR TANNING HIDES COMPRISING THE STEPS OF PARTIALLY TANNING THE HIDES WITH A NON-VEGATABLE TANNING AGENT FOR SEVERAL HOURS TO SEPARTE THE FIBERS, MECHANICALLY EXPRESSING WATER FROM THE PARTIALLY TANNED HIDES TO REDUCE THE WEIGHT OF THE PARTAILY TANNED HIDES TO AN AMOUNT AT LEAST 30% LESS THAN THE ORIGINAL WEIGHT OF THE HIDES, AND TANNING THE HIDES WITH A VEGETABLE TANNING EXTRACT SELECTED FROM THE GROUP CONSISTING OF DRY, POWEDERED TANNING EXTRACTS AND CONCENTRATED SOLUTIONS THEREOF FOR SEVERAL HOURS UNTIL THE TANNING EXTRACT HAS BEEN ABSORBED BY THE HIDES IN AN AMOUNT ABOUT EQUAL TO THE WEIGHT OF THE WATER REMOVED DURING THE EXPRESSION STEP. 